A magnetic thin film having excellent soft magnetic properties at several tens of MHz is desired for use with a magnetic head for high-density television (HDTV) which requires a high transmission rate or for other magnetic circuit components which are becoming more and more miniaturized. It is known that soft magnetic properties of metallic magnetic materials with high saturation magnetic flux density are greatly influenced by magnetocrystalline anisotropic energy, a magnetostriction constant, or a magnetic domain structure of the metallic magnetic materials. As a means to improve soft magnetic properties of metallic magnetic materials, it was proposed to reduce coercivity of a multilayer film comprising permalloy and non-magnetic materials being laminated to about one tenth of a monolayer (Nature, Vol. 194, pp. 1035, 1962). This method, which is theoretically explained by J. C. Slonczewski et al. (J. Appl. Phys., Vol. 37, pp. 1268, 1965), is known as the magnetostatic bonding effect because magnetostatic bonding is enhanced between magnetic layers sandwiched with non-magnetic layers through layers being laminated, and also because domain wall energy is reduced through controlling magnetic flux from leaking.
Recently, a magnetic thin film having improved soft magnetic properties was attained by dispersing metal magnetic crystal grains which are smaller than an exchange bonding length inside a thin film such that the orientation becomes random, and also by reducing apparent magnetocrystalline anisotropic energy through crystal grains being placed so close to each other that exchange bonding can take place between the magnetic metal crystal grains (IEEE Trans. Magn., Vol. 26, pp. 1397, 1990 etc.).
As a means to attain the above-mentioned nanocrystalline soft magnetic thin films, a method is known, in which magnetic crystal grains of several nanometer are deposited by conducting heat treatment to a metal magnetic thin film which contains a non-magnetic element and is in an amorphous condition (MAG-23,27,2746,1987). Another means, known as a manocrystalline effect, is a method of controlling manostructure by laminating a non-magnetic layer and a magnetic layer with the periodicity of several nanometers (Appl. Phys. Lett., 52,672,1988).
The above-mentioned theory of J. C. Slonczewski was applied in the past to improve soft magnetic properties by enhancing magnetostatic bonding through lamination of a material with high saturation magnetic flux density of more than 1.2 tesla. However, even if a non-magnetic layer is extremely thinned to about 1 nm. coercivity can be reduced only to about half of a single film. This is due to the fact that materials with high saturation magnetic flux density generally possess high magnetocrystalline anisotropy. Also, when a laminated film having this kind of non-magnetic layer of about 1 nm as this one is formed, for example, since interface free energy at the interface of non-magnetic layer / metal magnetic layer, such as SiO.sub.2 / Fe, is substantially large, a clear layer structure can not be obtained. Furthermore, if, for example, this is an interface of metal non-magnetic layer / metal magnetic layer such as Cu / Fe, when a heat treatment is conducted to this soft magnetic laminated thin film at the time of industrial application, the layer structure is destroyed even further due to layer-to-layer dispersion, and magnetic layers are bonded to each other directly. Thus, exchange bonding works between the magnetic layers, and magnetostatic bonding is no longer dominant, so that the problem arose that soft magnetic properties can not be improved as expected through a structural change in magnetic domain.
Conventionally, for a nanocrystalline magnetic thin film to be formed to minute crystal grains of less than exchange bonding length, when this thin film is applied to a type of depositing minute crystal grains from an amorphous condition, saturation magnetic flux density is small at low temperature still with the amorphous condition. Furthermore, when the temperature of heat treatment is too high, heat stabilization of the soft magnetic properties is bad because the grains grow larger than the grain size for the exchange bonding length, so that the specific temperature of heat treatment is generally restricted to about 500.degree. C.
Due to this, for example, when a magnetic thin film was applied to a magnetic head, it was not possible to use highly reliable glass having a high melting point in the process of heat treatment due to glass fusion of the head. As a result, the problem arose that the yield of head production and reliability of the head itself could not be improved. In addition, since the temperature of heat treatment was restricted, different properties were attained by differences in the temperature of the heat treatment.
Furthermore, when a nanocrystalline magnetic thin film comprising a non-magnetic layer and a magnetic layer, which were laminated with the periodicity of several nanometer orders is used, growth of grains can be controlled by thickening the non-magnetic layer, so that it is possible to improve stability of heat treatment, but saturation magnetic flux density becomes low because the ratio of the non-magnetic materials occupying the entire magnetic body becomes higher. Moreover, the non-magnetic layer, which is present between the magnetic layers, deteriorates the exchange bonding in the direction perpendicular to the film surface. In addition, the magnetic layer which grows on the surface of a non-magnetic layer by means of vapor deposition tends to grow oriented to a specific crystal surface, so that magnetic crystal grains which are adjacent to each other in the direction perpendicular to the film surface via a non-magnetic layer no longer have crystal surfaces at random to each other. Therefore, the problem with this was that the apparent magnetocrystalline anisotropy was not sufficiently lowered, and the soft magnetic properties were not improved.
Furthermore, when a magnetic thin film is used which combines the above-mentioned magnetostatic bonding effect and the manocrystalline effect, namely, when a magnetic thin film is used which is formed by laminating a non-magnetic layer having sufficient thickness for attaining magnetostatic bonding in the direction perpendicular to the film surface and a magnetic layer having crystal grains with an average diameter of several nanometers inside the film surface such as when the magnetic layer itself was thinned to several nanometers for miniaturizing the diameter of crystal grain inside the film surface, the problem arose that the apparent saturation magnetic flux density became smaller. When this aspect was compensated by using a material having high saturation magnetic flux density such as ferrite, the problem with this was that protection against corrosion sufficient for practical use could not be attained.
In addition, in view of industrial productivity, the speed of film formation needed to be controlled in order to produce a magnetic thin film with high yield comprising extremely thin films of several nanometers to several tens of nanometers which were laminated, and thus using conventional techniques, the production efficiency could not be improved.